Add client composition mode to RanchuHWC

... to help with Cuttlefish backports to Q/R branches.

Bug: b/216827224
Test: `cvd start --gpu_mode=gfxstream` with
      "androidboot.hardware.hwcomposer.mode=client"
Change-Id: I3afe75edf58b7668f3a5c237dcdc0320db128555
6 files changed